Chapter 4 Compounds and Their Bonds

Transcription

1 Chapter 4 Compounds and Their Bonds 4.1 Octet Rule and Ions Octet Rule An octet is 8 valence electrons. is associated with the stability of the noble gases. He is stable with 2 valence electrons (duet). valence electrons He 2 2 Ne 2, 8 8 Ar 2, 8, 8 8 Kr 2, 8, 14, Ionic and Covalent Bonds Metals Form Positive Ions Atoms that are not noble gases form octets to become more stable. by losing, gaining, or sharing valence electrons. by forming ionic bonds or covalent bonds. Metals form positive ions by a loss of their valence electrons. with the electron configuration of the nearest noble gas. that have fewer electrons than protons. Group 1A metals ion 1+ Group 2A metals ion 2+ Group 3A metals ion Formation of a Sodium Ion, Na + Charge of Sodium Ion, Na + With the loss of its valence electron, the sodium ion has a 1+ charge. Na atom Na + ion 11p + 11p + 11e - 10e , 8 5 6

2 Formation of Mg 2+ Charge of Magnesium Ion, Mg 2+ Magnesium achieves an octet by losing its two valence electrons. With the loss of two valence electrons, magnesium forms a positive ion with a 2+ charge. Mg atom Mg 2+ ion 12p + 12p + 12e- 10e A. The number of valence electrons in aluminum is 1) 1e -. 2) 2e -. 3) 3e -. B. The change in electrons for octet requires a 1) loss of 3e -. 2) gain of 3e -. 3) a gain of 5e -. C. The ionic charge of aluminum is 1) 3-. 2) 5-. 3) 3+. D. The symbol for the aluminum ion is 1) Al 3+. 2) Al 3-. 3) Al +. A. The number of valence electrons in aluminum is 3) 3 e -. B. The change in electrons for octet requires a 1) loss of 3e -. C. The ionic charge of aluminum is 3) 3+. D. The symbol for the aluminum ion is 1) Al Formation of Negative Ions Formation of a Chloride, Cl - In ionic compounds, nonmetals in Groups 5A (15), 6A (16) and 7A (17) Chlorine achieves an octet by adding an electron to its valence electrons. achieve an octet arrangement by gaining electrons. form negatively charged ions with 3-, 2-, or 1- charges

3 Charge of a Chloride Ion, Cl - Ionic Charge from Group Numbers By gaining 1 electron, the chloride ion has a 1- charge. Chlorine atom, Cl Chloride ion, Cl 17p + 17p + 17e - 18e The charge of a positive ion is equal to its Group number. Group 1A(1) = 1+ Group 2A(2) = 2+ Group 3A(3) = 3+ The charge of a negative ion is obtained by subtracting 8 or 18 from its Group number. Group 6A(16) = 6-8 = 2- or 16-18= Some Ionic Charges A. The number of valence electrons in sulfur is 1) 4e -. 2) 6e -. 3) 8e -. B. The change in electrons for octet requires a 1) loss of 2e -. 2) gain of 2e -. 3) a gain of 4e -. C. The ionic charge of sulfur is 1) 2+. 2) 2-. 3) A. The number of valence electrons in sulfur is 2) 6e -. B. The change in electrons for octet requires a 2) gain of 2e -. Chapter 4 Compounds and Their Bonds 4.2 Ionic Compounds C. The ionic charge of sulfur is 2)

4 Ionic Compounds Salt Is An Ionic Compound Ionic compounds consist of positive and negative ions. have attractions called ionic bonds between positively and negatively charged ions. have high melting and boiling points. are solid at room temperature. Sodium chloride or table salt is an example of an ionic compound Ionic Formulas Charge Balance for NaCl, Salt An ionic formula consists of positively and negatively charged ions. is neutral. has charge balance. total positive charge = total negative charge The symbol of the metal is written first, followed by the symbol of the nonmetal. In NaCl, a Na atom loses its valence electron. a Cl atom gains an electron. the symbol of the metal is written first, followed by the symbol of the nonmetal Charge Balance in MgCl2 Charge Balance in Na 2 S In MgCl 2, a Mg atom loses 2 valence electrons. two Cl atoms each gain 1 electron. subscripts indicate the number of ions needed to give charge balance. In Na 2 S, two Na atoms lose 1 valence electron each. one S atom gains 2 electrons. subscripts show the number of ions needed to give charge balance

14 Carbon Forms 4 Covalent Bonds Multiple Bonds In a CH 4 (methane) molecule, 1 C atom shares electrons with 4 H atoms to attain an octet. In a nitrogen molecule, N 2, each N atom shares 3 electrons. each N attains an octet. the bond is a multiple bond called a triple bond. the name is the same as the element. each H atom shares 1 electron to become stable, like helium Naming Covalent Compounds Guide to Naming Covalent Compounds In the names of covalent compounds, prefixes are used to indicate the number of atoms (subscript) of each element. (mono is usually omitted) Naming Covalent Compounds Naming Covalent Compounds What is the name of SO 3? 1. The first nonmetal is S sulfur. 2. The second nonmetal is O, named oxide. 3. The subscript 3 of O is shown as the prefix tri. SO 3 -> sulfur trioxide The subscript 1 (for S) or mono is understood. Name P 4 S The first nonmetal, P, is phosphorus. 2. The second nonmetal, S, is sulfide. 3. The subscript 4 of P is shown as tetra. The subscript 3 of O is shown as tri. P 4 S 3 -> tetraphosphorus trisulfide 83 84

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